Moody Sounds BJF Honey Bee OD kit (HBOD)
designed by Bjorn Juhl (BJFe) w/quality components
Moody Sounds BJF Honey Bee OD kit
official BJFe Honey Bee Overdrive kit (HBOD)
Honey Bee Overdrive kit
This model came about in 2002. It begun with a Guitar show and a 2 year anniversary as I was working on a possible circuit and I really wanted to make medium gain distortion but as luck had it an old friend of mine that is a pedal hater came with his newly acquired Supro amp that was dead from a blown power transformer. My friend said “make something that sounds like this amplifier or like the amplifiers we used to play when we were young, the kind that did not distort enough and that did not have enough treble…” As work progressed my friend said “get rid of that frequency it sounds like a pedal”. And so slewrate limiting techniques were called for but eventually the circuit was too dark and so it was given a ”3dB filter” that allegedly makes guitar amps sound good. This is a filter that has a slow slope of 3dB and that gives a staircase- due to this phase through the filter and that make the filter have less impact on final sound and yet raise treble mildly.
This model was supposed to be made in just one unit but it got to be three units eventually. Number 2 and 3 were fitted with a trimpot that was not used on any unit later on. Honey Bee was an obscure rare model handmade in Sweden up unitil 2009 when a DIY forum advertised via google to get one to take apart and popularity exploded after that with multiple clones and DIY kits but this is the first official BJF kit.
The voltage amplifier
The heart of the Honey Bee overdrive kit circuit is a CA3130 CMOS OP amp, that is particular in that it internally is almost entirely made with CMOS transistors (except for the VAS Voltage Amplifier Stage that is a bipolar transistor). Due to the CMOS technology max power supply voltage seen at pin 6 is 15V’s. However this OP amp has an output swing close to supply rails which at 9V gives near 8V’s pk-pk output as compared to standard OP amps 5,5V pk-pk. Noise performance is medium but the VAS has been overcompensated to reduce wideband noise and R7 ensures a minimum resistance at input in case input is shorted to ground and its value roughly corresponds to source resistance of minimum noise. FET/CMOS input OP amps has very low input currents and can handle large impedances and high signal levels and under such conditions they show better noise performance than bipolar OP amps that in turn can have lower noise but only at lower impedances and lower levels and further FET/CMOS Op amps handle overload slightly better than bipolar OP amps.
The tone response
The sound is sum of dynamic distortion created with multiple clipping points and filters to restrict overtones. Feedback network around the OP amp is made in three parts. Initially two clamping diodes, two low current LED’s with a forward voltage of 1,7V limit output swing and they will clip gradually and also limit current through clamping diodes D5, D6 making a gradual onset of distortion rather than a rapid. The point of clamping diodes D5, D6 is stale and low impedance and serves as feedback entry point via a bass boosting filter made with C8 and R11. At the other end R8 and C6 for a treble boosting filter that can be negated with C5. After clamper D5, D6 follows a lowpass filter and from there again a bass boosting feedback making a step slope. The net effect is bandpass filter where the bass slope can be moved and at max bass circuit becomes a lowpass filter. The highpass section is set above any fundamental note on a bass and the relative level of of fundamental notes can be set with the Tone control. Initially all notes are amplified and distorted with the clampers but nearly all overtones are fed back and nulled via the summing of the differential inputs of the OP. This hinders the the output slewrate and so at low input level sound is close to bypass but as input level increases the circuit distorts but most of the overtones are filtered out and result is distortion with mostly the lowest order overtones and higher order overtones are filtered out.
Now output of the last filter is fairly high impedance and it is isolated with an amplifier made with a JFet. So the purpose of T1 is to isolate the filters from the 3dB filter.
The Control knobs
The very first Honey Bee Overdrive took output from the source at N1 via a 2,2uF capacitor via 47K//4n7 into a 50K Linear volume pot. This resulted in low output however output can also be taken from Drain at a higher level.
Circuit was given a tone control called Nature and this was a 50K log that had viper to ground and terminal 1 to N1 and terminal 3 to one end of a 4n7 capacitor that had the other end connected to junction of R19//C13 and terminal 3 of volume pot so as to null the 3dB filter when Nature was set to max (fully CW).
The Honey Bee Overdrive kit can be wired for Treble and Bass control where N1 and N2 each get a 50KC connected as reostat to ground and C14 made 22nF and R18 2K0.
To get more gain R8/C6 can be adjusted. The very first Honey Bees used 1K and 100nF but after a while some wanted more ”guitar midrange” and so corner frequency was shifted down one octave to 1K and 220nF.
Later a rockabilly guitarist wanted more treble and Nature was wired with terminal 3 to N2 and C14 made 220nF and R18 = 4K7. In 2020 this was changed to 22nF and 2K0 to make treble shimmer rather than upper midrange.
People have asked how to get more gain out of the circuit and the way to do that is to adjust R8/C6. The lower the value of R8 the more gain. But C6 needs to follow so for twice the gain make R8 = 470R and double the value of C6 to 220nF or 470nF for four times the gain divide R8 by 2 and multiply C6 by 2.
To allow more overtones C8, C9 can be halved in value to shift response up one octave.